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Meiosis

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Meiosis

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  1. Meiosis Honors Biology Spring 2013

  2. Warm-Up • With a neighbor, discuss the following: • What is meiosis? • How does it differ from mitosis?

  3. Essential Questions What is meiosis and why is it necessary? What are the stages of meiosis? How does meiosis compare to mitosis?

  4. Haploid vs. Diploid Diploid cells 1. Body cells 2. Contains homologous chromosomes 3. 2N B. Haploid cells 1. Sex cells 2. contains one member of each pair 3. 1N

  5. Meiosis • Meiosis • process which reduces by half the number of chromosomes in a diploid cell • meiosis occurs in sex organs of individual

  6. Overview of Meiosis A. Meiosis - formation of sex cells 1. Meiosis is cell division that results in a gamete containing half the number of chromosomes of its parent. 2. Meiosis includes 2 steps that each closely resemble corresponding steps in mitosis.

  7. Phases of Meiosismeiosis I • Prophase I • Metaphase I • Anaphase I • Telophase I &? • CytokinesisPMAT I • Meiosis II • Prophase II • Metaphase II • Anaphase II • Telophase II &? • Cytokinesis PMAT II

  8. Meiosis 1 Meiosis I - reduction division 1. Interphase I 2. Prophase I 3. Metaphase I 4. Anaphase I 5. Telophase I

  9. Meiosis 1: Prophase 1 • chromatin condenses to form chromosomes • homologous chromosomes attach to form tetrads

  10. Meiosis 1: Prophase 1 • when tetrads form, crossing over can occur • crossing over is the exchange of part of homologous chromatids

  11. Meiosis 1: Metaphase 1 • tetrads line up on equator • spindle fibers attach to centromeres

  12. Meiosis 1: Anaphase 1 • homologous chromosomes separate • spindle fibers pull them to opposite poles

  13. Meiosis 1: Telophase and Cytokinesis • telophase I • nuclear membrane reforms • cytokinesis • cytoplasm splits

  14. Meiosis 1: Results • results • two haploid (n) daughter cells = ½ the number of chromosomes as parent cell

  15. Meiosis II Meiosis II - separation of chromatids 1. Interphase II 2. Prophase II 3. Metaphase II 4. Anaphase II 5. Telophase II

  16. Meiosis II: Prophase II • chromosomes already formed

  17. Meiosis II: Metaphase II • chromosomes line up along equator

  18. Meiosis II: Anaphase II • sister chromatids separate • move to opposite ends

  19. Meiosis II: Telophase and Cytokinesis • telophaseII • nuclear envelope reforms • cytokinesis • cytoplasm splits

  20. Meiosis II: Results • 4 haploid (n) daughter cells • all genetically different

  21. Ploidy • parent cell? • dipliod (2n) • after meiosis I? • haploid (n) (monopliod) • after meiosis II? • hapliod (n)

  22. Purpose of Meiosis: Diversity • Meiosis and sexual reproduction significantly contribute to genetic variation among offspring.

  23. Purpose of Meiosis: Gametes • role of meiosis is to produce gametes • meiosis in males • spermatogenesis • produces 4 sperm cells • meiosis in females • oogenesis • produces 1 ovum (egg cell) and 3 polar bodies

  24. Where Does Meiosis Occur?

  25. Mitosis vs. Meiosis • where does is occur? • meiosis – sex organs; mitosis – somatic cells • number of cell divisions? • meiosis – 2; mitosis – 1 • number of cells produced? • meiosis – 4; mitosis – 2 • ploidy of daughter cells? • meiosis – hapliod (n); mitosis – dipliod (2n) • # of chromosomes compared to parent cell? • meiosis – ½ # chromosomes; mitosis – same

  26. Mitosis vs. Meiosis